1. Field
Example embodiments relate to a memory device and a method of manufacturing the same. Other example embodiments relate to a memory device including a hydrophilic second tunneling oxide layer and nanocrystals and a method of manufacturing the same.
2. Description of the Related Art
A memory device using a semiconductor includes a transistor and a capacitor. The transistor functions as a switch that provides a path for a current when recording or reading information. The transistor is placed in the capacitor. The capacitor preserves stored charges.
A substantially high transconductance is necessary in order for the transistor to allow a substantially large amount of current to flow through. As such, a metal oxide semiconductor field effect transistor (MOSFET) having a substantially high transconductance is used as a switching device of a semiconductor memory device. The MOSFET includes a gate electrode, source electrodes and drain electrodes. The gate electrode is formed of multi-crystalline silicon. The source and drain electrodes are formed of doped crystalline silicon.
As information devices develop, there has been an increase in research focused on developing smaller, highly-integrated memory devices (e.g., devices in which the number of integrated memory devices per unit area is increased). If such highly-integrated memory devices are used, then the signal transmission time between devices is reduced. As such, a larger amount of information is processed at a higher speed.
In a conventional MOSFET, a larger amount of heat is generated. As such, if the integration of the memory device increases, then the device may melt or malfunction.
A single electron device (SED) has been developed. Theoretically, a SED uses electrical signals by transmitting one electron. As such, a device is required to more precisely control the transmission of the electron. A nanocrystal may be used to control the transmission of the electron.
The nanocrystal may be formed of a metal or semiconductor that has a smaller size than a Bohr exiton diameter (e.g., a few nanometers). A nanocrystal has a large number of electrons, yet the number of free electrons is limited to about 1-100.
The energy potential of the electrons in a nanocrystal is limited. As such, a nanocrystal shows different electrical and/or optical properties than a nanocrystal formed of a metal or semiconductor in a bulk state, which forms a continuous band.
Conventionally, various conductors and nonconductors are mixed in order to obtain semiconductors having a desired band gap. Nanocrystals have different energy potentials which vary according to the size of nanocrystals. The band gap may be controlled by changing the size of the nanocrystals.
Unlike a bulk-type semiconductor, the amount of energy needed for adding electrons is not uniform but varies in a stepwise manner. A Coulomb blockade effect, in which the present of an existing electron disturbs the addition of new electrons, may occur.
If there are a desired number of electrons needed for crystals, then the transfer of additional electrons by tunneling is blocked. If the size of the nanocrystals is less than 10 nm, then theoretically a single electron can be transferred. Because the number of transferred electrons is smaller, the amount of heat generated is also smaller. Because less heat is generated, smaller device can be manufactured.
The nanocrystals may be used in smaller devices if used with a transistor. Research has been conducted on memory devices having nanocrystals.
Conventional nanocrystals used in memory devices are manufactured by heat treatment. Nanocrystals having a higher melting point may not be treated with heat. The size of the nanocrystals manufactured by heat treatment is not uniform. Nanocrystals that are not uniform deteriorate characteristics of the memory device.